There has been much progress for this problem in the setting of planar domains, and we refer the readers to [1]}, [2]}, [3]}, [4]} and references therein for a complete bibliography. An important contribution was made in the planar case by [4]} to introduce rigor into the computation of [2]}. The use of layered potential in [4]} also cast this problem in the mainstream language of elliptic PDE and facilitates some of the approach we use in this article.
